The invention relates generally to semiconductor fabrication and more specifically to a semiconductor processing chamber designed to remove and preclude moisture from a region above a semiconductor substrate within the chamber in order to rapidly transition between pressure states within the chamber.
Semiconductor manufacturing systems are constantly being designed with an eye towards improving throughput. For example, processing chambers have been configured in the form of a cluster tool in order to permit the integration of multiple steps of a process. These systems generally include other chambers for handling and transporting wafers between modules operating at atmospheric pressure and vacuum to ensure a clean process environment and improve throughput by eliminating the need to vent the processing chamber during wafer transfer steps. During the processing of a semiconductor substrate, the substrate is transported into and out of a load lock, which is a chamber that cycles between vacuum and atmospheric pressure. When the substrate is placed in the load lock from an atmospheric transfer module (ATM), the load lock will be at atmospheric pressure. The air in the load lock is then pumped out to provide a vacuum in the load lock chamber. The substrate is then transported to the processing chamber via a vacuum transfer module by a robotic arm. The processing operation (e.g., etching, oxidation, chemical vapor deposition, etc.) is then performed in the processing chamber.
After the substrate has been processed, the robotic arm in the vacuum transfer module moves the substrate back to the load lock, which is in a vacuum condition from the transfer discussed above. Once the substrate is placed in the load lock, the pressure in the load lock is brought back to atmospheric pressure by venting in a gas such as nitrogen (N2). When atmospheric pressure has been achieved, the processed substrate is transported to a substrate cassette for other processing steps, if necessary. In semiconductor processing, the value of a process system depends to a large extent on the rate at which substrates can be processed. That is, a process system with a higher throughput will produce more processed substrates in a given amount of time than a system with lower process rate. Thus, the process system with the highest throughput is the more desirable system with all other features being equal.
However, the throughput of semiconductor process systems depends largely on the speed with which chambers, such as a load lock, can be cycled between low and high pressure. For the cluster architecture described above, the load lock is the chamber transitioning between different pressure states, therefore, the time to cycle the load lock is crucial to the system throughput. Unfortunately, the cycle speed of a load lock chamber in conventional process systems is generally limited by the rate at which the load lock can be cycled between a vacuum state and an atmospheric state without depositing particles on a substrate. In particular, the transition from an atmospheric pressure to a vacuum state inside the chamber is limited by the rate at which vacuum is pulled in the chamber. That is, condensation of moisture is avoided by limiting the rate at which a vacuum is pulled in the chamber. Moisture, in the form of airborne water vapor, will condense as the temperature drops below the dew point temperature as the vacuum is pulled. The individual water droplets can nucleate about a particle entrapped in the air and, because of the weight of the nucleated mass, fall onto the substrate if the vacuum is pulled at too fast of a rate. The water is eventually boiled off as vacuum is pulled, however, the particle is left on the surface of the substrate as a contaminate which may eventually lead to device failure. The contaminated substrate can negatively impact semiconductor yields.
FIG. 1 is a schematic diagram of a load lock. Load lock 100 includes access ports 102, bottom vacuum port 104, and bottom vent port 106. Within load lock 100, is wafer support 110 having pads 112 on which a semiconductor substrate 108 rests on when inside the load lock. Of course, pads 112 can be pins. It will be appreciated by one skilled in the art, that load lock 100 transitions between differing pressure states. For example, if wafer 108 has been processed, then the wafer 108 is typically introduced into load lock 100 under a vacuum state. The vacuum state is then broken through the introduction of gas through bottom vent port 106. Once the pressure in load lock 100 is brought to an atmospheric pressure, the wafer is then transferred out of load lock 100 to an atmosphere transport module. If wafer 108 is unprocessed, then the wafer is introduced into load lock 100 from an atmospheric transport module to the load lock while the load lock is at atmospheric pressure. Load lock 100 is then pumped out through vacuum port 104 to create a vacuum within the load lock.
However, one of the shortcomings of the design of load lock 100 is that when either of access ports 102 are open, external moisture from outside the load lock will enter through either of the open access ports. Thus, when load lock 100 is pumped out to create a vacuum, moisture 116, i.e., water vapor, that has entered the chamber through access ports 102 will reside in a region 114 over wafer 108. As mentioned above, if a vacuum in the load lock is pulled too quickly, water vapor 116 will condense in region 114. This condensation can nucleate around a particle in region 114 and eventually fall onto a surface of wafer 108, thereby contaminating the wafer.
An additional shortcoming with the design of load lock 100 is that when a gas is vented in through bottom vent port 106, particulate matter which has fallen to the chamber bottom in the vicinity of the chamber inlet of bottom vent port 106 can be entrained in the gas flow. That is, any sufficiently light particulate matter on the bottom of chamber 100 can be kicked up during a venting operation. Thus, the entrained particulate matter can deposit on a substrate within the load lock thereby leading to lower yields.
One attempt to solve the problem of the condensation falling on top of the surface of wafer 108, is to restrict the rate at which a vacuum is pulled within load lock 100. That is, a vacuum is pulled in two steps, with the first step at a slower rate, so as not to cross a dew point to avoid creating condensation. However, restricting the vacuum rate also restricts the throughput of the system.
In view of the foregoing, there is a need to improve the cycling rate of the load lock between pressure states to allow for a higher throughput without exposing a substrate to contaminants.
Broadly speaking, the present invention fills these needs by providing a chamber capable of rapidly cycling between differing pressure states without exposing a wafer inside the chamber to contaminates. The present invention also provides a method for conditioning an environment above the wafer inside the chamber.
In accordance with one aspect of the present invention, a method for conditioning an environment in a region defined above a semiconductor substrate within a pressure varying interface is provided. The method initiates with a semiconductor substrate being introduced through an access port into a pressure varying interface. The pressure varying interface is at a first pressure. Then, moisture from a region defined above the semiconductor substrate is displaced. In one embodiment, the moisture is displaced by introducing a dry fluid through a top vent port of the pressure varying interface. Next, the access port is closed. Then, a pressure within the pressure varying interface is transitioned to a second pressure. Next, the semiconductor substrate is transferred from the pressure varying interface.
In accordance with another aspect of the invention, a method for minimizing moisture in a region above a semiconductor substrate in a chamber is provided. The method initiates with providing a vent port extending through a top surface of a chamber. Then, a vacuum port extending through a bottom surface of the chamber is provided. Next, moisture is inhibited from entering a region defined over a semiconductor substrate positioned on a support within the chamber. Then, a pressure within the chamber is transitioned to a vacuum, wherein condensation forms outside of the region defined over the semiconductor substrate during the transition to a vacuum.
In accordance with another aspect of the present invention, a chamber for transitioning a semiconductor substrate between modules operating at different pressures is provided. The chamber includes a base defining an outlet. The outlet permits removal of an atmosphere within the chamber to create a vacuum. A substrate support for supporting a semiconductor substrate within the chamber is included. A chamber top having an inlet is included. The inlet is configured to allow for the introduction of a gas into the chamber to displace moisture in a region defined above the substrate support. Sidewalls extending from the base to the chamber top are included. The sidewalls include access ports for entry and exit of a semiconductor substrate from the chamber.
In accordance with yet another aspect of the present invention, a system for processing a semiconductor substrate is provided. The system includes a first transfer module configured to operate at a first pressure and a second transfer module configured to operate at a second pressure. A pressure varying interface in communication with the first and the second transfer modules is included. The pressure varying interface is capable of transitioning between the first and the second pressures. The pressure varying interface includes a top vent port and a bottom vacuum port. The top vent port is configured to introduce a fluid into the pressure varying interface, wherein the introduction of the fluid displaces moisture in a region defined above a semiconductor substrate in the pressure varying interface.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.